It is inevitable that it will cost money (a fee) to use a debit or credit card and as well there is a cost that the retailer puts into the cost of the item you buy to cover the fee they are charged
So as you have to pay make it as small as possible, because the fees appear to vary greatly
Ultimately to pay by cash (at the moment) costs nothing and I have not read any legislation that says you can be charged extra for using cash, that ability to do so by the retailer was previously illegal
There are other non bank cards which could be cheaper than banks so check them out
